This invention relates to Glan-laser prisms used in laser systems and more particularly to a Glan-laser prism polarizer wherein the prism elements are surrounded by a fluid with an index of refraction matching fluid with the gap filled by the fluid.
Heretofore Glan-Thompson prisms have been used in laser systems. Glan-Thompson prisms are formed by two prisms cemented together at their interface. In use, these prisms were found not acceptable for use in high power lasers because the cement used could not withstand the high power. In order to solve the problem, the prisms were not cemented together and were positioned with an air gap in between the prisms. Such elements are known as a Glan-laser prism.
Crystals normally used for Glan-laser prisms are calcite. This material is a naturally occuring crystal having indexes of refraction of the birefringent crystal of 1.66 and 1.49. Calcite has a very high damage threshold, however, the cost of very high quality material are not readily available at any cost.
Since large Calcite prisms are not available, Glen-laser prisms have been constructed from 90% deuterated potassium dihydrogen phosphate (KD*P). KD*P has a small birefringence and is very hydroscopic; however, it has a damage threshold higher than quartz, it can be grown commercially in large strain free pieces, and it is very transparent at 1.06M, which is a desired operating wavelength. KD*P Glan-laser polarizers have been found to be good polarizers, but they suffer from low transmission and severe fringing of the output beam.
It has been determined that the between-prism gap (whose sides because of low birefringence are necessarily very parallel), acts like a shear-plate interferometer. Since the desired polarity compound of the light beam must operate very close to its critical angle, a substantial amount of the energy through the prism is in the unwanted first forward reflected beam. Since the gap is at an angle to the beam, and since the laser must operate with a diverging wavefront at useful levels, the result is unacceptable deep fringes on the transmitted beam.